It should not be possible to use amplitude variation with offset to detect hydrocarbons. Any physicist can tell you that the mathematical inversion of even the most perfect AVO data is nonunique. I often take pride in my ability to beautifully model prestack gathers for giant gas fields without requiring VP/VS ratios of the kind expected for gas-bearing rocks. In fact, any AVO anomaly can be explained with an appropriate combination of nonreservoir rocks.

So AVO doesn't work. Right? Wrong. There are places in the world where an exploration well is not drilled unless there...